Field of the Disclosure
This disclosure relates to components for turbochargers having a bearing housing between a turbine housing and a compressor housing. More particularly, this disclosure relates to a bearing housing having a shaped spacer and shaped core for inducing a swirling effect for defoaming oil.
Description of Related Art
Advantages of turbocharging include increased power output, lower fuel consumption and reduced pollutant emissions. The turbocharging of engines is no longer primarily seen from a high power performance perspective, but is rather viewed as a means of reducing fuel consumption and environmental pollution on account of lower carbon dioxide (CO2) emissions. Currently, a primary reason for turbocharging is using exhaust gas energy to reduce fuel consumption and emissions. In turbocharged engines, combustion air is pre-compressed before being supplied to the engine. The engine aspirates the same volume of air-fuel mixture as a naturally aspirated engine, but due to the higher pressure, thus higher density, more air and fuel mass is supplied into a combustion chamber in a controlled manner. Consequently, more fuel can be burned, so that the engine's power output increases relative to the speed and swept volume.
In exhaust gas turbocharging, some of the exhaust gas energy, which would normally be wasted, is used to drive a turbine. The turbine includes a turbine wheel that is mounted on a shaft and is rotatably driven by exhaust gas flow. The turbocharger returns some of this normally wasted exhaust gas energy back into the engine, contributing to the engine's efficiency and saving fuel. A compressor, which is driven by the turbine, draws in filtered ambient air, compresses it, and then supplies it to the engine. The compressor includes a compressor impeller that is mounted on the same shaft so that rotation of the turbine wheel causes rotation of the compressor impeller.
Turbochargers typically include a turbine housing connected to the engine's exhaust manifold, a compressor housing connected to the engine's intake manifold, and a center bearing housing coupling the turbine and compressor housings together. The bearing housing encloses the rotating shaft.
In an example radial bearing system, the shaft turns with minimal friction on an oil film in floating radial bearings. For the turbocharger, the oil supply is fed from the engine. The bearing system is designed such that floating radial bearings, rotating at less than shaft speed, are situated between the stationary bearing housing and the rotating shaft. This allows these bearings to be adapted such that there is no metal contact between shaft and bearings at any operating speed. Besides the lubricating function, the oil film also has a damping function, which contributes to the stability of the shaft and turbine wheel assembly. The oil may also remove heat from the turbocharger as the oil drains through an oil drain to a crankcase of the engine.
A through bore in the bearing housing for the rotating shaft extends from a compressor end to a turbine end of the bearing housing. The bearing housing includes bearings disposed at least partially in the through bore of the bearing housing and a bearing spacer. The shaft is rotatably supported by the bearings and has a rotational axis coincident with a rotational axis of the turbine wheel and a rotational axis of the compressor impeller. The bearing housing includes oil passages to direct oil from an oil inlet to the bearings and a shaft oil path to direct oil from the oil inlet to the rotating shaft in a manner dependent on rotational position of the bearing spacer in the through bore of the bearing housing. The spacer as shown in FIGS. 1 and 2 includes a single line of large apertures, specifically four apertures, processing around the center of the tubular spacer in a cylindrical oil drain cavity.
A core of the bearing housing includes an oil drain cavity between the oil inlet and the oil drain. The lubricating oil flows into the turbocharger at a pressure of approximately four bars. As the oil drains off at lower pressure, the oil drain diameter is typically larger than the oil inlet. The oil flow through the bearing is usually vertical from top to bottom. The oil should be returned into the crankcase above the engine oil level. Any obstruction in the oil drain will result in back pressure in the bearing system.
This disclosure focuses on oil in the bearing housing of turbochargers that can become agitated and foamed by the internal moving parts of the turbocharger. Agitated foamed oil can be detrimental to the proper function of the bearing housing oil drain cavity. Foamed oil has difficulty draining from the oil drain and other negative effects on the engine.